1. Field of the Invention
This invention relates generally to a device for determining the level of a cooled liquid in a closed container, and more particularly, to a cholesteric liquid crystal fluid level indicator that determines the level of a cooled liquid, such as beer, in a keg when placed in thermal contact with the exterior surface of the keg by producing a color change that is a function of the liquid temperature when the liquid is within a predetermined temperature range. The invention also produces a predetermined color when the liquid is within a predetermined temperature range for visually ascertaining whether it is at its ideal temperature.
2. Description of the Background Art
In the bar and restaurant industry, an accurate inventory is paramount to maintaining the bottom line and anticipated profit margins. When food and drink inventory are lost, it eats into the company's profit. Accordingly, restaurant owners and operators employ strict inventory tracking methods for food, liquor and controllables. For instance, food consumption is measured by noting counts per unit or weighing the food product. Specific emphasis is placed on the amount of pounds and ounces being sold and lost. Inventory for controllables, such as paper goods (paper towels, toilet paper, napkins, etc.), condiments (ketchup, mustard, sugars, Sweet-n-Low.RTM., sauces, etc.), glassware and miscellaneous items (straws, toothpicks, etc.) are also routinely counted. Liquor is accounted for by counting bottles and noting levels remaining in partially used bottles. In fact, most bar inventory methods count the bottles in tenths or quarters. This measuring technique is reasonably accurate since the liquor levels can be seen through the bottles. While accountable inventory measuring techniques exist for food, liquor and controllables, there is still no accurate, cost effective method or device for taking the inventory of draft beer in a closed keg.
Conventional techniques for taking inventory of draft beer are either inaccurate, unsafe, time consuming and/or too expensive. Draft beer is sold in opaque kegs. Therefore, beer levels can not be readily and accurately ascertained. Inventory for draft beer is primarily done by lifting and shaking the keg. Lifting and shaking kegs to determine the quantity remaining is highly subjective and inaccurate. It only provides an approximation of how much beer is left in the keg. Another method involves lifting and weighing the keg to determine the amount of beer remaining. Weighing the keg, while theoretically more accurate, requires a durable scale and additional information for converting weight to ounces. Neither method is convenient and both involve heavy lifting. As a full keg weighs approximately 160 pounds, there is a high risk of back injuries, muscle tears and hernias, associated with lifting, shaking and/or weighing kegs, even with a partially filled keg. An injured employee is inevitably lost for a period of time and a worker's compensation claim is invariably made, increasing the likelihood of increased insurance premiums. It is therefore desirable to have a device that measures keg fluid levels without requiring lifting, shaking or weighing. A device for readily measuring keg levels that avoids and solves the foregoing risks and problems would be well received.
Another problem experienced by restaurant and bar businesses is ascertaining whether beer in a keg is at its ideal temperature or at least within its required temperature range. The ideal temperature for beer varies. The ideal temperature for beer can range between 32.degree. F. and 44.degree. F. depending on the make and entity storing the beer. The ideal temperature for most beer is approximately thirty-eight degrees Fahrenheit (38.degree. F.). Microbrews and foreign beers can have ideal temperatures between 38.degree. F. and 42.degree. F. And, some establishments store their beer at temperatures below 38.degree. F. and as low as 32.degree. F. Therefore, most coolers are operated within this temperature range to keep the beer at its ideal temperature. In fact, many local health ordinances require that coolers be operated within a specified range, such as 35.degree. F. to 44.degree. F.
Beer kegs are stored in coolers, typically along with other items that are needed more frequently. Therefore, the temperature in a cooler constantly fluctuates due to the refrigeration system efficiency and frequent opening of the door. If the cooler is not operating properly or is experiencing a high flow of traffic, it can warm the cooler several degrees. This increase in temperature is typically unnoticeable to the individual, but still affects the temperature of the beer. If the cooler is allowed to operate outside its temperature for extended periods of time it can cause the beer to age prematurely. Conversely, some coolers may be operated too low, such as around 33.degree. F., to compensate for fluctuations in temperture. However, when traffic slows down for a period of time the beer can drop below its ideal temperature. If a device was ecomically available for monitoring the temperature of beer in a keg, the cooler could be adjusted to ensure that the beer is maintained at or near its ideal temperature. In fact, a beer level measuring device for kegs that also insures proper beer temperature would be well received by the industry.
Several devices are known in the background art for measuring propane levels in gas tanks. Other devices are known for measuring the temperature of liquids, such as wine. However, none of these devices are adapted for or capable of measuring the level of beer or other fluids in a closed keg or for indicating whether beer is at its ideal temperature, as contemplated by the instant invention. One known device comprises an electronic sonar device. This device is costly and outside the scope of the instant invention. Other devices known employ thermotropic or thermochromic liquid crystal technology for measuring gas levels in closed tanks, such as propane tanks. This technology has primarily been applied to flow visualization and heat transfer research. More recently, thermochromic liquid crystal technology has been used for thermometer strips, such as forehead thermometers, and propane tank gas measurement devices. These devices, however, are not designed for reacting to temperatures within the temperature range in which conventional coolers and walk-in refrigerators are operated, i.e. between 32.degree. F. and 44.degree. F. Such a device would facilitate convenient monitoring of a keg's beer level and indicate whether the beer is below, above or at its ideal temperature.
The most common thermochromic liquid crystal known to be employed with measuring gas in closed tanks is the cholesteric liquid crystal. Cholesteric liquid crystals are chemical compounds and mixtures which exhibit the mechanical properties of liquids but have the optical properties of crystals. Cholesteric liquid crystals are optically active mixtures of organic materials which produce color changes in reaction to fluctuations in temperature in a temperature range which is a function of the particular compound selected. Depending on the compound selected, changes from red to violet can occur in a range of +20.degree. C. to 250.degree. C. Known gas level monitoring devices are only designed to react to temperatures above 59.degree. F. The liquid crystal composition in theses devices can not react to exhibit colors between 30.degree. F. and 50.degree. F.
Cholesteric liquid crystals show color by selectively reflecting incident white light. In response to temperature differentials, conventional cholesteric liquid crystals change colors across the visible spectrum, beginning at colorless and going through red, orange/yellow (tan or brown), green, blue, violet and colorless again. Liquid crystal mixtures and products typically have a red start/transition temperature at one end of the bandwidth, a green mid-section and a blue start/transition temperature at the other end of the bandwidth. The bandwidth is determined by the difference between the red start temperature and the blue start temperature. The background art known for measuring gas in a tank comprises liquid crystal strips designed for bandwidths in higher temperatures that can not be triggered by the cooler temperatures needed for producing a color change for liquids in the 30.degree. F. to 50.degree. F. range. While thermometers exist for reading the temperature of wine and refrigerators, they are not adapted for attachment to a keg or for use in reading the level of beer in a keg. Liquid crystal thermometers only give one reading. These thermometers are also outside the temperature range for cooled kegs of beer and are not capable of reading the level of beer in a closed keg. Moreover, the liquid crystal technology employed in the background art requires that a temperature differential be induced on the article being tested by either heating or cooling the liquid crystal strip.
As currently employed for propane tanks, cholesteric liquid crystals and other thermochromic liquid crystals are designed for working in the 15.degree. C. to 50.degree. C. (59.degree. F. to 122.degree. F.) range. In fact, several patents have issued for devices adapted to tighter tolerances within this range or to different transition temperatures within this range. These devices fail to contemplate or address the indication of beer level in kegs and ideal temperatures. In addition, these known patents require that the strips containing the liquid crystals be heated or cooled to create a temperature differential. For instance, U.S. Pat. No. 3,696,675, issued to Gilmour, discloses a method and means for determining liquid level in a container comprising an elongated strip of material coated or imbedded with cholesteric liquid crystals which exhibit color changes with changes in temperature. The term liquid is used loosely in Gilnour. Gilmour is specifically designed for propane gas and thus operates in the mesomorphic range between 59.degree. F. and 122.degree. F. Gilmour also requires a temperature change to be induced on the exterior surface wall of the container by applying heated or chilled water or utilizing an electrical heating element. Parker, in U.S. Pat. No. 5,323,652, discloses a thermochromic level indicator comprising a temperature responsive strip including at least two thermochromic materials of different opacities and transition temperatures which produce a color in the 80.6.degree. F. to 95.degree. F. temperature range. Parker is also designed for measuring gas levels in propane tanks and requires that an external temperature source, such as hot water, an electrical heating element or a pair of leads carrying a current, be applied to the strip. Thomas et al., in U.S. Pat. No. 5,385,044, discloses a method of using a thermochromatic detergent level indicator for determining the level of solid detergent contents in an opaque, plastic container. Thomas et al. is specifically designed for solid detergents and uses a thermochromatic substance which has a temperature activity point ranging from 100.degree. F. to 180.degree. F. and requires an external water spray having a temperature of 120.degree. F. Heynderickx et al., in U.S. Pat. No. 5,686,153, discloses an optical temperature indicator comprising an optically active layer of a transparent polymeric material in which liquid-crystaline material is dispersed and has a polymeric structure which is based on siloxane. Heynderickx et al. is specifically designed for high temperatures, i.e. temperatures above 174.degree. F., for use with irons, coffee makers, hairdriers, elecrtrical cookers, ovens and deep-fat fryers. The Heynderickx et al. strip is blue below 174.degree. F. and red above this temperature. Paron et al. discloses a wine thermometer for adhesive application to wine bottles to determine wine temperature therein. The Paron et al. thermometer has a plurality of different liquid crystal compositions that make up a temperature panel that operates in the 40.degree. F. to 66.degree. F. range and has a temperature scale adjacent the panel. Similar to conventional thermometers, Paron et al. has a plurlaity of temperature levels and each level comprises a different liquid crystal composition for measuring different temperatures across the thermometer. Like the other above noted patents, Paron et al. requires an external temperature source, such as hot or cold water, to activate the liquid crystal strip thermometer. In addition, Paron et al. comprises a thermometer that only measures temperatures above the temperature range for cooled beer kegs.
The above noted art fails to teach or suggest a thermochromic liquid crystal strip that can measure the level of beer in a cooled keg. The above noted art is not operable within the 30.degree. F. to 50.degree. F. temperature range or adapted for use in reading beer level in a keg, and requires an external temperature source, such as hot or cold water or an electrical heating element, to work. There is no device currently known that measures the level of cooled liquids in a closed container and/or indicates whether the liquid is at its ideal temperature. Consequently, there exist a need for such a device. The instant invention specifically addresses this gap in the prior art by providing a thermochromic liquid crystal strip having a liquid crystal composition that produces color change somewhere in the 30.degree. F. to 50.degree. F. temperature range. This range is consistent with the temperature of beer so that the level of beer may be readily determined by observing the color change of the strip. In addition, the instant invention produces a predetermined color when the beer is at its ideal temperature to indicate the same.